1. Field of the Invention
This invention relates to an ultrasonic motor which utilizes a traveling wave for driving a moving member, and more particularly, relates to an improvement of a vibration member on which the traveling wave is generated.
2. Description of the Related Art
FIGS. 4 and 5 show a structure of a conventional ultrasonic motor. Further, FIG. 6 is a cross-section view of a vibrating member 6 which is installed in the conventional ultrasonic motor.
A ring-shaped vibrator 7 is adhered to the disc-shaped vibrating member 6. A moving member 2 is in contact with a contacting portion 6a of the vibrating member 6.
The vibrating member 6 is rigidly fixed, at its center, to a cover 11. The moving member 2 is pressed against the vibrating member 6 through a rubbery resilient member 4 by a spring 3. A spindle 1 is inserted into the center of the moving member 2 so as to support the moving member 2. The spindle 1 is rotatably supported by a pair of bearings 9a, 9b which are pressed into a case 10 and the cover 11.
When an A.C. electrical power source having a proper frequency and phase is applied to the vibrator 7, the vibrating member 6 is oscillated along a tangent direction .THETA., a normal direction z and radial direction r. The oscillations along the tangent direction .THETA. and the normal direction z generate a traveling wave which circulates along the contacting portion 6a of the vibrating member 6. The moving member 2 which is pressed to the vibrating member 6 rotates with the spindle 1 in accordance with circulation of the traveling wave.
In the conventional ultrasonic motor, the radial width a of the contacting portion 6a is smaller than the radial width b of the vibrating member 6 (i.e., width a.ltoreq.width b) so that energy of the vibration is concentrated to the contacting portion 6a. The output of the ultrasonic motor is increased if the energy of the vibration is concentrated to the contact portion 6a.
However, if the radial width a becomes too large compared with the radial width b, the amplitude along the tangent direction .THETA. is decreased. As a result of this, the moving member 2 rotates slowly and output of the ultrasonic motor is decreased.